The Washington Post newspaper celebrated the release of its Tehran bureau chief Jason Rezaian from prison at a ceremony attended by U.S. Secretary of State John Kerry.

Rezaian was released from a Tehran jail as part of a prisoner swap last week. He says his Iranian interrogators told him during his 18-month detention that the U.S. government wouldn't "lift a finger" for his release.

But Kerry was working behind the scenes to secure his release along with four other Americans held by Tehran -- winning Rezaian's tearful thanks.

Kerry told dignitaries attending the event in the Post's new headquarters on January 28 that Rezaian's detention weighed heavily on U.S. officials.

"This gnawed at us, because we sensed the wrongfulness and we knew that Jason and others were living the consequences," he said.

After embracing Rezaian, Kerry cited the military, saying that you "never leave a buddy behind."